1. Field of the Invention
The present invention relates to fluid flow equipment, and more particularly, to fluid flow controlling equipment such as compressors and pumps.
2. Description of the Related Art
The information described below is not admitted to be prior art by virtue of its inclusion in this Background section.
Fluid flow controlling equipment (xe2x80x9cfluid flow controllersxe2x80x9d) may be considered to include those apparatuses that are capable of controlling (e.g., pumping, compressing) fluid flow (e.g., liquids, gases, combinations thereof). Two of the most important types of fluid flow controllers are pumps and compressors. Pumps are fluid flow controllers that may be used to raise and/or transfer fluids, often by pressure or suction. Compressors are fluid flow controllers that may be used to increase the pressure of a fluid (typically gases). There are several types of pumps and compressors. Many compressors and pumps have overlapping characteristics (e.g., many types of each are similar in design), and thus the device types are usually distinguished by their primary intended use.
One particularly important type of compressor is the centrifugal compressor. Centrifugal compressors typically operate by accelerating a fluid introduced into the compressor and then decelerating the fluid to induce a rise in the fluid static pressure. The principle of operation behind a centrifugal compressor is similar to that of a centrifugal pump; the difference is essentially in the nature of the fluids operated on by each device. Centrifugal compressors are often preferred over other compressor types because of their potential for smaller size and greater pressure rise.
Centrifugal compressors typically include an impeller, or rotor, positioned within a stationary casing (e.g., a stator). In a typical centrifugal compressor configuration, the rotor is essentially a wheel with curved vanes, or blades. The blades extend from the hub of the rotor to the tip of the rotor. The hub of the rotor has hub opening that extends through the rotor. A shaft for rotating the rotor within the casing extends through the hub and is attached to the rotor. During operation, fluid flow typically enters a centrifugal compressor in a direction substantially parallel to the rotational axis of the rotor, and exits the rotor in a direction substantially perpendicular to the rotational axis of the rotor. By appropriately rotating the rotor within the casing, the blades of the rotor may accelerate fluid fed into the compressor, allowing the fluid to exit the rotor with increased velocity (and possibly pressure). The accelerated fluid may then be directed into a collector (e.g., a volute). From the collector, the accelerated fluid may enter a diffuser where the fluid is slowed, allowing further conversion from kinetic energy (velocity) to potential energy (pressure) to occur.
In a centrifugal compressor, the degree of fluid flow acceleration is largely affected by the orientation of the blades on the rotor. Generally speaking, rotor blades can be oriented in radial, forward (flow directed into the direction of rotation), or backwards (flow directed opposite the direction of rotation) orientations. By orienting the blades in a particular manner, and by otherwise molding the rotor blades into particular shapes (e.g., twisting or leaning the blades), fluid directed into a compressor can be turned a certain way by the rotor and a desired degree of fluid acceleration can be obtained.
Unfortunately, the extent to which the orientation of rotor blades may be effectively manipulated to enhance fluid flow acceleration is limited. As noted above, conventional compressor blades may extend from a point proximal the hub of the rotor to a point proximal the rotor tip. When attempting to accelerate fluid with such blades, the rotated fluid preferably follows a blade or blades of the rotor for the length of the blade(s). That is, in an ideal centrifugal compressor entering fluid travels along a blade from the inner edge of a blade to the outer edge of the blade before exiting the rotor into the collector. If, however, the angles of the rotor blades are too large, and the rotated fluid is turned to an excessive degree (given a variety of fluid and compressor parameters), then the fluid may not follow (e.g., may separate from) the rotor blades. The separated fluid may increase the turbulence of the fluid sent into the collector, making the fluid flow more difficult to handle efficiently. Such a situation may undesirably prevent the desired degree of acceleration (and thus pressurization) from being achieved.
In an attempt to circumvent this problem, many compressor designers are forced to abandon more compact, single stage designs in favor of larger, multiple stage designs. Multiple stage compressors typically include multiple rotors arranged in series to obtain greater pressure rises than may usually be obtainable from single stage compressors using the same type of rotor. Because such multiple stage compressors are larger, however, one of the advantages of using a centrifugal pump may be reduced or lost. In addition, the efficient transport of an accelerated fluid from one stage to another is difficult, and thus the efficiency of multiple stage compressors is often less than a similarly configured single stage compressor.
Therefore, it would be desirable to develop a fluid flow controller, e.g., a compressor or pump, which has an enhanced ability to accelerate fluid flow. Such a fluid flow controller should reduce or eliminate the need to use multiple stages to achieve a desired degree of performance.
The problems described above may be in large part addressed by the present fluid flow controller and method of operation thereof. The fluid flow controller may include a casing having a casing blade. The fluid flow controller may also include a rotor including a first rotor blade and a second rotor blade. The first and second rotor blades are preferably truncated such that they are radially spaced from each other. That is, the first and second rotor blades preferably do not extend the length of the rotor (e.g., from the hub of the rotor to the tip of the rotor) as do many conventional blades, but instead each extend to radially spaced points along the rotor. The casing blade is preferably also a truncated blade having a length less than the radial spacing between the first and second rotor blades. Thus, the rotor may be configured to rotate relative to, and preferably within, the casing such that the casing blade passes between the first and second rotor blades during use.
Compared to conventional pumps or compressors, the present fluid flow controller may have an enhanced ability to accelerate (and possibly to subsequently pressurize) fluid flow. As noted above, when the angles of a rotor blade become too extreme, and the rotated fluid is turned to an excessive degree (given a variety of fluid and controller parameters), the fluid may not follow the rotor blades and the desired degree of acceleration may not be obtained. In addition, the maximum extent to which rotor blades may efficiently turn fluid flow is influenced by the length of the blades. Thus, the maximum degree to which each truncated blade can turn or accelerate fluid flow may be slightly less than that of a conventional rotor blade that extends from the rotor hub to the rotor tip. But since the number of discrete blades on the rotor and casing may be significantly increased over conventional designs, the present fluid flow controller may provide greater fluid flow acceleration.
One reason for this benefit may be that each blade of the present fluid flow controller (whether on the casing or the rotor) may be configured specifically for the flow characteristics it is expected to encounter during operation. Further, instead of having to be turned by, and thus follow, one long, continuous blade over its entire length, fluid flow may instead be turned by several discrete blades in series. In addition, because of the presence of the casing blades between the rotor blades, the velocity of fluid flow leaving a first rotor blade may have no necessary relationship to the velocity of fluid flow entering a second radially spaced rotor blade (e.g., the casing blade may turn fluid flow to a different direction and/or velocity than it had leaving the first rotor blade). Thus, the orientation of the second rotor blade may not be limited by the orientation of the first rotor blade. By configuring the blades appropriately, the sum acceleration imparted by the series of rotor and casing blades may be significantly greater than that provided by a single continuous blade. Beneficially, such increased acceleration may reduce or avoid the need to resort to multiple stage designs when, e.g., very large pressure rises are desired.
In an embodiment, the fluid flow controller may include a centrifugal pump or compressor having a casing in which a rotor is configured to rotate. The casing may have at least one casing blade, and preferably has a plurality of casing blades. The fluid flow controller may further include a rotor. The rotor may also include at least first and second radially spaced rotor blades. Preferably, the rotor includes a first plurality (e.g., a first row) of rotor blades and a second plurality (e.g., a second row) of rotor blades radially spaced from the first row of rotor blades. The rotor may be positioned within the casing, and may be configured to rotate within the casing such that each of the casing blades passes between the first and second plurality of rotor blades during use. That is, the rotor blades may, by rotation of the rotor to which they are attached, rotate around the casing blades such that at some point in time each of the casing blades is positioned between a rotor blade from each plurality of rotor blades. The first and second pluralities of rotor blades may be further configured to turn and accelerate fluid flow. The casing blades may also be configured to turn and accelerate fluid flow. The casing blades may be located within the circumference (i.e., within the lateral boundaries of) the rotor.
During use, fluid flow may be introduced into the casing, within which the rotor may be positioned. The rotor may be rotated to accelerate the fluid flow. In an embodiment, the fluid flow may be turned by a first rotor blade from the first plurality of rotor blades, then by a casing blade, and then finally by a second rotor blade from the second plurality of rotor blades. As noted above, the amount of acceleration and/or compression imparted to a fluid passing through the rotor/casing assembly may consequently be much higher than is conventionally possible. The casing may be connected to a volute configured to collect fluid flow exiting the rotor, and further to diffuse the fluid flow (e.g., in a diffuser section) to induce a pressure rise therein. Fluid flow that has been accelerated and/or compressed by the rotor may subsequently pass into the volute and out the volute exit, to be used in whatever manner desired.
In a preferred embodiment, the rotor may have a hub configured to receive a shaft for rotating the rotor. The hub may include a hub opening through which the shaft may extend. The hub may protrude from a base of the rotor (e.g., the bottommost portion of the rotor), and preferably widens as it approaches the rotor base. The first plurality of rotor blades may be arranged closer to a center of the hub than the second plurality of rotor blades. The casing blades are preferably sized such that they are thinner than the minimum radial spacing between the first and second plurality of rotor blades. Thus, the casing blades may pass between the first and second plurality of rotor blades during rotation of the rotor within the casing.
Preferably, the rotor is a centrifugal or mixed flow (i.e., between axial and centrifugal) rotor. Thus, the rotor is preferably configured to accelerate fluid flow such that the predominant orientation of fluid flow exiting the rotor during use is angled away from and substantially oblique to the rotational axis of the rotor. That is, the majority of fluid flow exiting the rotor during use may have an orientation angled away from the rotational axis of the rotor by an amount greater than 5, and preferably greater than 10, degrees. More preferably, the rotor may be configured to accelerate fluid flow such that the predominant orientation of fluid flow exiting the rotor during use is substantially perpendicular to the rotational axis of the rotor (e.g., within 10, and preferably 5, degrees of perpendicular).
To achieve the flow characteristics described above, the rotor may be shaped such that the diameter of the hub increases from the top of the hub to the rotor base. Consequently, the hub may have a sloped or curved surface beneath the rotor blades that, when travelling from a point near the center of the hub to the tip of the rotor, starts in a orientation substantially parallel to the rotational axis of the rotor, and ends in a orientation substantially perpendicular to the rotational axis of the rotor. In an embodiment, each of the rotor blades may include an outer end and an inner end closer to the center of the hub than the outer end. The rotor may thus be configured such that a diameter of the rotor at a point proximal to the inner ends of the second plurality of rotor blades is greater than a diameter of the rotor proximal to the inner ends of the first plurality of rotor blades. More preferably, a diameter of the rotor at a point proximal to the inner ends of the first plurality of rotor blades may be less than a diameter of the rotor at a point proximal to the respective outer ends of the first plurality of rotor blades. Further, a diameter of the rotor at a point proximal to the inner ends of the second plurality of rotor blades may be less than a diameter of the rotor at a point proximal to the respective outer ends of the second plurality of rotor blades.
Consequently, the fluid flow controller may include a fluid flow path defined between the casing and the rotor that is preferably substantially parallel to the axis of rotation of the rotor at the inlet of the fluid flow path and is preferably substantially perpendicular to the axis of rotation of the rotor at the outlet of the fluid flow path. The inlet of the fluid flow path may be an opening in the casing defined above the center of the rotor hub, and the outlet of the fluid flow path may be located near the tip of the rotor. At the outlet of the fluid flow path, the accelerated and/or compressed fluid may have a substantially radial, or centrifugal, orientation.
Preferably, the casing blades are closely positioned between blades of the first and second rows of rotor blades during use. Consequently, the spacing between the casing blades and the rotor blades, and between the casing blades and the rotor surface, as a casing blade passes between the first and second row of rotor blades may be relatively small. In an embodiment, the spacing between the casing blades and the rotor surface may be approximately equivalent to the spacing between the rotor blades and the casing surface from which the casing blades extend.
In other embodiments, the fluid flow controller could incorporate different numbers of blades in the first and second rows of rotor blades. The casing could also contain more or fewer casing blades than either row of rotor blades. The rotor and casing blades can be angled in a variety of manners (e.g., radially, forward, or backwards), and can be angled in different directions even within the same cohort of blades. The ability to vary the number and orientation of blades in the casing and/or the rotor to any desired degree (depending on the expected fluid flow conditions and the desired outcome) may allow for further enhancement of the efficiency of the present fluid flow controller. Embodiments showing specific potential variations will be explained in more detail below.
In addition, a dual rotor design is presented in which the rotor is configured as a rotor assembly having a first rotor and a second rotor configured to independently rotate. The first rotor may have a first rotor blade, and the second rotor may have a second rotor blade. The second rotor preferably has a diameter greater than the first rotor. Preferably, the first rotor is positionable at least partially within the lateral boundaries of the second rotor such that the first rotor blade is radially spaced from the second rotor blade. In an embodiment, the rotor assembly may be configured to accelerate fluid flow such that the predominant orientation of fluid flow exiting the rotor assembly during use is angled away from and substantially oblique to, and more preferably substantially perpendicular to, a rotational axis of the rotor assembly.
A fluid flow controller including such a rotor assembly may have several advantages. In addition to the features and benefits of the embodiments described above, a dual rotor assembly may allow the rotational speed of the rotor blades on each rotor to be independently set to a speed dependent on the specific needs of that row. In an embodiment, the first rotor and the second rotor may each be attached to separate and possibly concentric shafts, allowing the first and second rotors to be rotated at different velocities. For example, the second, outer rotor may be rotated at a lower speed than the first, inner rotor, potentially improving the efficiency of the fluid flow controller. In addition, the first and second rotors may be rotated in opposite directions.